Our proposed research is multiphasic and includes: The effect of artificial cardiac pacing on control of bradycardias and tachycardias; the influence of drugs on threshold to pace, cardiac output and intracardiac voltages; the clinical course of paced patients, including underlying rhythm, pacemaker modification, morbidity and mortality; the functional reliability and utility of existent pacing equipment and development of new equipment of improved flexibility, utility, reliability and longevity toward the "ideal pacemaker"; definition of causes of malfunction, electrical, electronic, magnetic, unusual intracardiac currents; the utility of electronic "clinic" and transtelephone methods of monitoring; to set up a computerized record and retrieval system for the massive clinical, electronic and physiologic data we develop to speed data analyses and reporting. Our objectives are: 1) To make pacemakers flexible, reliable, long lasting; 2) To prolong life in as near physiologic function as possible; 3) to understand better the interrelationship of pacing and the patient; 4) To set standards of safety and performance. This year will emphasize computer analysis of the data of 1000 patients, tests of new pacemakers (Medtronic programmable pulse duration, Cordis programmable Omnicors and atomic powered generators) and life extension of pacer systems.